This invention relates to a process and apparatus for piecing yarn on a spinning unit of an open-end friction spinning machine having a large number of spinning units. Spinning units of the type contemplated by the invention each contain two rollers that are drivable in the same rotational direction and are arranged next to one another and form a wedge-shaped gap serving as a yarn spinning or forming region. At least one suction device affects the wedge-shaped gap and there is also provided a feeding device for the feeding of single fibers to the wedge-shaped gap, a yarn withdrawal device for withdrawing the formed yarn, and a winding device for the winding of the yarn onto a spool.
A manual piecing process is known in the case of an open-end friction spinning unit--see European Published Unexamined Patent Application (EP-OS) No. 34 427. In the case of this spinning unit, only one of the two rollers is constructed as a so-called suction roller, which is provided with a perforated shell and a suction insert arranged in its interior and aiming at the wedge-shaped gap with a suction slot. The second roller has a closed shell surface. During the piecing, the wind-up roller is lifted off its operational drive, after which the broken yarn end is found and unwound manually and shortened to a predetermined length. This length is such that the end of the yarn end reaches the yarn forming point, i.e., arrives in the area of the mouth of one of the fiber feeding channels opposite the wedge-shaped gap. After the cutting to length, the yarn end, while avoiding the withdrawal device of the spinning unit, is led to a yarn withdrawal tube, from where it is sucked into the spinning unit because the vacuum of the suction device affecting the wedge-shaped gap is maintained. By the manual operation of a covering of the suction insert, the yarn end is to be sucked into the spinning unit, while the suction slot of the suction device is gradually closed so that the suction effect is switched off at the end of the insertion process. The yarn end must then be held by a suction withdrawal device arranged as an extension of the wedge-shaped gap. After the suction device is switched on again by the opening of the covering of the suction slot, the yarn end should arrive in the wedge-shaped gap. If possible, the feeding of the fibers is to be started at the same time as the suction device is switched back on, after which the yarn withdrawal is resumed by the placing of the wind-up spool on its driving roller. Then the newly pieced yarn is manually placed in the withdrawal device. The yarn piecing produced during the piecing process is wound onto the spool. By means of this process, yarn piecings cannot be obtained which have a good enough quality compared with the quality of the normally spun yarn to be left in the yarn when the yarn is processed further. Rather these piecings must be cleaned out and replaced by another yarn connection on a spooling machine before a further processing of the yarn.
In the case of open-end rotor spinning machines--see German Patent (DE-PS) No. 29 39 644--it is known to carry out a piecing process by means of a travelling servicing apparatus at a spinning unit during full production speed, where the obtained yarn piecing, before the winding-up of the pieced yarn, is detached by the drivable servicing apparatus and is replaced by a knot. The yarn produced during the knotting is sucked into a pneumatic yarn-storage device existing at each spinning unit. Apart from the fact that a yarn connection in the form of a knot will hardly be accepted in modern machines, the known type of piecing cannot be carried out in open-end friction spinning because operating speeds exist there which correspond to about three times the operating speeds in the case of open-end rotor spinning machines. During the making of the yarn connection, yarn production continues, without the occurrence of a winding process. In the case of the high operating speeds, quantities of yarn would occur which could either not be stored in a yarn storage device or could not be stored there properly.
The invention is based, at least in part, on the objective or providing a process and a device or apparatus for piecing a yarn at individual spinning units of an open-end friction spinning machine that can be carried out fully automatically and that ensures that the spools of yarn produced on the open-end friction machine can be further processed directly without having to be subjected to another work step.
This objective is achieved according to the invention by providing an arrangement wherein a yarn end that is brought into the wedge-shaped gap is pieced with incoming fibers to form a yarn piecing. The yarn piecing is detached from the yarn before a renewed winding-up of the yarn and is replaced by a yarn connection connecting the newly produced yarn with the yarn leading to the spool, where the production of the yarn piecing takes place with control of the friction effect of the rollers, the quantity of the fed fibers and the withdrawal speed. The yarn production rate is reduced as compared to the normal spinning operating speed, wherein the normal spinning operating values are reached only after the yarn connection with the newly formed yarn has been made. The yarn spun during the making of the yarn connection is received by a yarn storage device, and the winding-up after the making of the yarn connection takes place at a wind-up speed which exhibits a higher speed difference with respect to the withdrawal speed than the normal spinning operational wind-up speed exhibits with respect to the normal spinning operational withdrawal speed.
The invention is based, at least in part, on the recognition that it is feasible in open-end friction spinning to also spin at a production speed that is much lower than the operational production rate, even as low as, for example, only ten percent of the operational production rate. The individual process steps can therefore be carried out relatively slowly so that the design requirements for the controlled timed element operations need not be too high, especially since the yarn piecing produced during the piecing process is subsequently detached and discarded and is not wound onto the spool of finished yarn. The yarn quantities occurring during the low production speed that must be stored during the making of the yarn connection can then be handled. Since the winding-up of the newly spun yarn takes place at a speed that permits a high difference in speed as compared to the withdrawal speed, which is higher than the normal speed difference during the normal spinning operation, the storage device can be emptied in a relatively short time so that overall the working time of a servicing apparatus required for a piecing process at a spinning unit can be kept relatively short.
According to a further aspect of preferred embodiments of the invention, it is provided that for the production of the yarn piecing or immediately after the production of the yarn piecing, the friction effect of the rollers, the quantity of the fed fibers and the withdrawal speed are adjusted to values that are reduced with respect to the normal spinning operational values, said reduced values being adapted to one another in such a way that during this phase, a yarn is spun which, in regard to the yarn count, corresponds to the normal operationally spun yarn. As a result, it is ensured that the yarn that is supplied to the yarn storage device and is subsequently wound onto the spool does not differ from the yarn produced during normal spinning operations. In this case, it can be provided according to certain preferred embodiments that the production of the yarn piecing itself takes place at a production speed which furnishes a yarn count that does not correspond to the yarn count spun at operational conditions, but only ensures that a successful piecing process takes place. Since the yarn piecing is detached and is not wound onto the spool and since, after the production of the yarn piecing, the same yarn count is spun as under operational conditions, yarn of the same yarn count will be wound onto the spool only later after the yarn piecing section has been discarded.
In certain preferred embodiments of the invention, it is provided that the friction effect of the rollers, the quantity of the fed fibers, and the withdrawal speed during the increase to their operational values (run-up phase) are adapted to one another in such a way that during this phase a yarn is spun having a yarn count that corresponds to the yarn spun at the operational values. This ensures that the yarn spun during the run-up phase that is wound onto the spool also corresponds exactly to the yarn spun under operational conditions.
In a further development of certain preferred embodiments of the invention, it is provided that the changing of the friction effect of the rollers, the increasing of the quantity of the fed fibers and the increasing of the withdrawal speed to the operational values takes place with a time delay with respect to the start of the spool winding-on process. As a result, the emptying of the yarn storage device takes place relatively rapidly since the emptying of the storage device takes place or is at least started at the low production speed.
In a further development of certain preferred embodiments of the invention, it is provided that for the reduction of the friction effect of the rollers, the rotating speed of the rollers is reduced. In another development or possibly in addition, it is provided that for the reduction of the friction effect of the rollers, the suction effect of the suction device is throttled.
In a further development of certain preferred embodiments of the invention, it is provided that the yarn end to be entered into the wedge-shaped gap is drawn off the spool, is returned into the spinning unit against the withdrawal direction and after the production of the yarn piecing in the shape of a loop is led to a suction withdrawal device, after which the portion of the loop containing the yarn piecing is cut out, and subsequently the ends of the loop are twisted together to form a yarn connection at a splicing mechanism separate from the friction rollers. In this case, during the twisting-together to form the yarn connection, the continuously produced and withdrawn newly spun yarn is directed to a yarn storage device that in running direction is located behind the withdrawal device and in front of the twisting section, said yarn, after the twisting-together, being withdrawn from the yarn storage device by the switching-on of the wind-up device. In the case of this embodiment, the yarn end withdrawn from the spool of the spinning unit is used directly, as needed, after a corresponding preparation of its extreme end, for carrying out the piecing process.
According to another development of preferred embodiments of the invention, it is provided that a yarn end having a predetermined length is introduced into the spinning unit in the withdrawal direction, is inserted into the wedge-shaped gap and, while the yarn piecing therewith is being produced, is withdrawn with the newly spun yarn in the withdrawal direction and is guided away in a suction withdrawal device. Subsequently the newly spun yarn, after being detached at least up to the yarn piecing, is twisted (spliced) together with a yarn end removed from the spool. In this case, during the twisting operation, the newly spun yarn is stored in a yarn storage device arranged in front of the twisting point and behind the withdrawal device, the yarn storage device being emptied after the twisting-together by the switching-on of the wind-up device. In the case of this process, a yarn end is introduced into the wedge-shaped gap in the withdrawal direction which is possible because with the production of the yarn piecing, the final connection to the yarn already wound-up on the spool is not yet established. In this case, it is useful according to contemplated preferred embodiments to remove the yarn end introduced into the spinning aggregate for the piecing, in the withdrawal direction, by means of an auxiliary spool. Auxiliary yarn may be used which clearly differs from the yarn to be spun in the normal spinning operation, out which advantageously significantly facilitates the piecing itself.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, embodiments constructed in accordance with the present invention.